On account of the steadily increased production out and manufacturing accuracy evolving in the course of technical development, and the growing demands on performance and quality especially of automobile gear drives, such machines are being employed more and more in industrial gear manufacture for grinding the flanks of pre-cut, hardened gear teeth. The most important aims targeted here are a high load carrying capacity of the tooth flanks in the interest of a compact weight and space saving gear unit design, and an optimum running smoothness, i.e. a minimum noise emission from the gear unit. Both demand a highly accurate observation of the desired flank form.
In continuous generation grinding the grinding worm and the teeth of the gear to be ground are in mutual generative engagement, wherein the workpiece is rotated strictly synchronous to the continuous rotation of the grinding worm at a speed ratio of the number of starts on the grinding worm to the number of teeth on the workpiece. Any deviation from this synchronism leads to form deviations of the workpiece flanks, and thereby impairs the workpiece quality.
One of the sources of synchronism deviation in the rotations of the grinding worm and workpiece which is difficult to control is the non-uniform running of the workpiece during grinding, caused by the tooth engagement of the driving pinion with the cylindrical gear on the work spindle, and the torque pulsation of the work drive motor. In the case of the tooth mesh disturbance, this results in a periodic rotational angular deviation of the workpiece teeth of an order related to the number of teeth on the work spindle gear, and in the case of the motor pulsation in a periodic rotational angular deviation of the workpiece teeth of an order related to the motor pulsation multiplied by the ratio of the numbers of teeth on the work spindle gear and the pinion.
Noise investigations with assembled gear units have shown that in the case of an integer transmission ratio between motor and work spindle, both orders of disturbance are clearly audible as tones in the noise level of the gear unit, both on the test stand and in the installed state in the vehicle, the frequencies of the two tones corresponding exactly with the order related to the tooth engagement of the work spindle gear and that of the pulsation of the spindle drive motor. This effect is still present even with the minimum possible motor pulsation and scarcely measurable rotational angular error of the work spindle gear, and requires for its elimination a costly re-machining of the workpiece teeth by lapping or honing in an additional machining operation, thus substantially increasing the manufacturing expense.
TAIZ, B. A, “Typical Errors in Gear Machining (part I)”, in “Fertigungstechnik und Betrieb”, 17th year, H.3, March 1967, pp. 180-187, recognizes that cyclic errors in the grinding worm produce an undulation on the tooth surface of the gear being machined. A proposal for a remedy is not given however.
In DE 23 46 530 a suggestion is made to provide an idler as primary gear, in order to improve the pitch accuracy.